Saturday, March 13, 2010

How to Supersize a Human

If all this sounds colossally unfair, well, it is. But even if the genetic deck is stacked against you, you’d probably escape unharmed were it not for the cooperation of a seriously skewed environment.

After all, obesity is a recent phenomenon—so recent that worldwide obesity statistics stretch back less than a generation. In the wild, virtually no other species experiences true obesity. Not only do humans break the mold, we also have the dubious distinction of being the only species to bring obesity to other animals, such as our overfed pets, livestock, zoo dwellers, and experimental subjects.

So what’s gone wrong in our world to shift a huge number of people— the majority in many countries—into excessive weight? Although there’s no definitive answer, it seems overwhelmingly likely that a set of factors work together to help make us fat. The following sections explain what they are.

Changes in activityFor tens of thousands of years, humans spent the better part of the day in activities we’d call exercise, with only the occasional period of rest. Today, the balance has neatly flipped, and our bodies are left sitting around like an idling automobile engine for most of the day.

Changes in foodAt the same time that we’ve switched from lives of restless activity to permanent relaxation, we’ve changed the way we fuel our bodies. Generations ago, we had no choice but to fill up with natural, unrefined foods that took a fair bit of digestive effort to convert to energy (and fat). By comparison, even the healthy eaters of today down huge quantities of processed, highcalorie, high-carbohydrate foods, which contain enough energy for an Olympic rowing team.

The breakdown of food cultureStudies show that people who eat a diet traditional to their native culture fare better than average eaters. This is true whether the culinary tradition is Greek, Italian, Japanese, French, or something else—even though all these diets are dramatically different and many emphasize sometimes stigmatized foods like pasta, rice, fatty meat, or butter.

There are two possible explanations. One is that the diet most Westerners eat—heavy on processed convenience foods—is, biologically speaking, the worst possible rubbish we could use to fuel ourselves. The other possibility is that people who are part of a traditional food culture are also guided by firm, unwritten rules that govern acceptable eating practices.

For example, consider the so-called French paradox—the fact that French people have a relatively low incidence of heart disease, despite enjoying a diet rich in cheese, cream, and other sources of saturated fat. Unlike North Americans, French eaters are part of a dining culture that emphasizes slow, shared meals. It discourages second helpings and snacking. And if you think you’ve got it bad, consider the plight of cultures that have moved from ancient cuisine to Western convenience foods in a single generation. Two examples are the desert-dwelling Pima Indians and the settlers of the tiny Micronesian island of Kosrae. Both populations are small, genetically similar, and cut off from the rest of the world. For generations, they lived through periods of intermittent famine that were more severe than those faced by most Europeans. Today, they’ve adopted a Western diet and suffer from staggering rates of obesity and diabetes, far worse than the rest of modern society. Scientists are still battling over whether the problem is environmental (for example, the population is particularly susceptible to Western conveniences because their old way of living and eating is obsolete) or genetic (perhaps they have a higher incidence of genes that spur overeating).

Environmental programmingIt’s a bit speculative, but many obesity researchers believe environmental cues during pregnancy or childhood activate certain genes in the body, putting a process in motion that ultimately leads to adult obesity. It’s not a far stretch—after all, not only have people been fattening up generation after generation, they’ve also been growing much taller and reaching sexual maturity far sooner. In studies of strains of obese rats, a brief period of underfeeding in infancy reduces their fatness in adulthood. A similar diet in later life has only temporary effects.

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In its broadest sense, science (from the Latin scientia, meaning "knowledge") refers to any systematic knowledge or practice. In its more usual restricted sense, science refers to a system of acquiring knowledge based on scientific method, as well as to the organized body of knowledge gained through such research.

Fields of science are commonly classified along two major lines: natural sciences, which study natural phenomena (including biological life), and social sciences, which study human behavior and societies. These groupings are empirical sciences, which means the knowledge must be based on observable phenomena and capable of being experimented for its validity by other researchers working under the same conditions.